Whenever you makes changes to your existing tools files or library files in
your server.., it will ask you to restart the Mysql server to see the effects.
So, given is the commands that will help you to Start and Stop and Restart MySQL
Database Server.

Upgrade MySQL 5.1 to 5.5 in cpanel
Upgrade MySQL5.1 to 5.5 in cpanel How to upgrade mysql5.1 to 5.5... 5.1 to 5.5 using cPanel. I have already tested on one of my server and it works well.
You can check the process at cPanel upgrade MySQL5.1 to 5.5.
Thanks